LED Resistor Calculator

Calculate the series resistor for one or more LEDs using supply voltage, forward voltage, and target current. Includes nearest E24 resistor value and expected current.

Calculator

Inputs

Supply voltage (V) LED forward voltage (V) LEDs in series Target current (mA)

Results

Calculated resistor—

Nearest E24 resistor—

Expected current (E24)—

Resistor voltage drop—

Resistor power—

Recommended resistor rating—

Enter circuit values.

Formula and practical notes

Basic formula: R = (Vs - N×Vf) / I. If remaining voltage is not positive, the selected number of LEDs cannot be driven from that supply in series. Choose resistor power with safety margin (commonly at least 2× calculated dissipation).

FAQ

Can I run LEDs without a resistor?

Usually no. Without current limiting, LED current can rise quickly and damage the LED.

Why use nearest E24 value?

Real circuits use standard resistor values. E24 provides practical parts you can buy easily.